EXPERIENCES CULTIVATING WHITE SHRIMP IN THAILAND

Transcription

1 EXPERIENCES CULTIVATING WHITE SHRIMP IN THAILAND Dr. Chalor Limsuwan Aquaculture Business Research Center Faculty of Fisheries, Kasetsart University, Thailand Summary of presentations in Peru, Colombia, and Guatemala, in February Prepared by: Nicovita-Alicorp Technical Service Introduction During his visits to several shrimp operations in Peru, Colombia, and Guatemala, Dr. Chalor Limsuwan issued several recommendations based on his experience in the cultivation of white shrimp Litopenaeus vannamei en Thailand. Stocking density in Thailand is currently animals/m², with aeration rates of HP/ha. Thailand exports 85% of the shrimp produced. Due to the current world economy unrest, the country will voluntarily decrease shrimp production by 20%, from 500,000 MT to 400,000 MT in 70,000 hectares, with 2-3 annual cycles. Thailand has implemented a partial-harvest-based production strategy at both 12 and 18 g, with final harvest at 24 g. The Thai government has mapped production zones so that harvests are organized on a perarea basis, making the most of US demand seasonality/sizes. Based on this strategy, producers have implemented good size management, resulting in increased profitability. Pond bottom preparation in the face of high organic matter concentrations In areas where organic matter builds up (channels and corners only) sodium nitrate is applied at the rate of 7.5 kg/ha. After every regular production cycle, the application of 2.5 kg sodium nitrate/ha and 60 kg calcium hydroxide/ha is recommended On organic matter-rich, sandy bottoms, soil compaction using an 8-inch PVC pipe full with sand is recommended after tillage. Bottom tillage should be performed when soil contains a certain level of moisture as to encourage bacterial activity Post-larval quality Good post-larval (PL) quality is a top priority in Thailand. Larvae should reach 10 g in 60 days, 17 g in 90 days, or 25 g in 120 days, all at stocking densities of PL/m 2, with 80% survival rate, at temperatures of C (from February to October). Positive rheotaxis (counter-current swimming) is a good larval quality control test. While water revolves in the test container, those remaining in the center are considered poor quality larvae. Salinity dictates stocking stage. For salinities between 25 and 35 (parts per thousand, ppt), PL10 respond well. For other salinity ranges, stocking the pond with PL12 is April - June

2 recommended, particularly for low salinity waters. Larval stage is identified based on the number of spines found in the dorsal aspect of the rostrum (Figure 1). Thai hatcheries expose the PLs at 32 C for 7 days, for them to become resistant to white spot syndrome virus (WSSV) during grow out. Figure 1. Determination of larval stage based on rostral spines. PL9 shows 3 spines in the rostrum. PL10 has a 4th spine being formed. PL12 is identified by its fully-developed 4th dorsal spine. Stocking Variations of 0.5 points in ph, temperature and salinity are recommended between hatchery larval dispatch and farm arrival time. In-transit ph is regulated using calcium bicarbonate. For fresh water cultivation, hatcheries deliver the larvae already acclimated to 5 salinity. This is why pre-stocking acclimation in the grow out pond is performed regarding only the temperature, so that this process takes no longer than one hour. The best stocking time is 6-7 AM or 6-7 PM, when the temperature is adequate and sun rays are milder, resulting in minimum larval stress. A common error among producers is the lack of precision to estimate the amount of larvae stocked. All excesses supplied by the hatchery must be taken into account when determining the amounts of larvae being stocked. This factor is important to estimate both pond biomass and feed amounts to be offered throughout the grow out cycle. At pond arrival, the total amount of larvae included in the bag must be counted. April - June

3 Water quality Proper water quality values for shrimp cultivation are as follows: Oxygen: 4.0 ppm O 2 during the daytime / 6.0 ppm in the afternoon ph: 7.5 in the morning / 8.5 in the afternoon. Alkalinity: ppm CaCO3 Non-ionized ammonium: max 0.1 mg/l Nitrites: max 0.01 mg/l Shrimp grow best at 28 C-31 C, with salinity levels Flaccidity problems can be due to Mg: Ca ratio imbalance. A 3.4:1.0 ratio is recommended in the face of medium to high salinity levels, and 5.0:1.0 for low salinities. For this purpose, dolomitic lime or magnesium chloride are suggested as magnesium sources. Feeding A good feeding program should result in: Low production cost Reduced FCR Good water quality Improved pond bottom Good shrimp growth Feeding program during the first month: In Thailand, a first-month feeding program is based on the amount needed for one million larvae. On day one, 2.5 kg feed are given. Thereafter, feed amounts are as follows: 2-7 days 100g /day (Feed amount on day 7: 3.1 kg) 8-14 days 200g/ day days 300g/ day (Feed amount on day 30: 9.3 kg) Total cumulative feed in the first 30 days of culture: kg. April - June

4 After the first month, feeding trays are used together with a table, based on biomass %: Shrimp weight (g) % Feeder management The best way of feeding shrimp is using feeders, referring to a feeding table. The feeder should not be used as the only reference. Interpreting feeder readings can be misleading because shrimp move around different parts of the pond. Errors can also result from feed losses derived from aeration movements, water flow, or too heavy weight feeders. When the feeder is located in the same direction of the flow, using a protective baffle is recommended (Figure 2). Figure 2. Feeder baffle to be used in the event of water current that could potentially displace the feed out of the tray April - June

5 The amount of feed per feeder and checking time based on shrimp weight is shown in the following table: Weight (grams) Feed g / kg /tray Checking times (hours) Feed % protein In intensive cultures in Thailand, % protein depends on cultivation stage, as follows: Weight (g) % Protein no less than: % % % % % % > % This percent protein is a function of good management, natural productivity, and the primary/secondary productivity balance, floc included. Good productivity occurs when diatoms prevail in the plankton, and pond water transparency is cm. Feed dose rate/timing Feeding the shrimp 4 times (4X) per day is most efficient. Suggested times follow: Feeding No. 1st 2nd 3rd 4th Times :00 AM 12: AM 05:00 PM 10:00 PM ( 30% of one ration) Feeding shrimp at 6:00 AM is not recommended because oxygen levels are typically too low. In the event that O 2 levels at 7:30 AM are still too low, then offering the feed later in the day is suggested, until oxygen levels improve. Offering a maximum of 30% of one ration in the night forces shrimp to consume the natural productivity. In the event of strong rain, feeding should be avoided due to potential sudden temperature/salinity fluctuations. Also, in the event of mass phytoplankton death, feeding should be avoided due to potentially-high ammonium/nitrite levels. Lastly, feeding rates April - June

6 should be lowered during molting. Calcium chloride is applied sometimes for the molting process to occur normally. Intestine/feces evaluation Evaluating shrimp intestine color is a variable tool for feeding management. Black intestines mean that shrimp are only eating natural productivity, while brown intestines are full of balanced feed. One hour after feeding, at least half of the shrimp should have the intestines full of feed. Otherwise, if all intestines are black, ration amounts must be increased. On the other hand, one hour after feeding intestines must be black, meaning that all feed from the previous dosing has been totally consumed, thus avoiding overfeeding. Overfeeding Overfeeding results in excess nutrients in the water which cause algal over-bloom. Algae will die later on when oxygen or nutrient levels decrease. When this occurs during cultivation, at least one feeding must be skipped thus pushing shrimp to consume natural productivity (benthos and detritus from dead algae). This way, shrimp growth is not affected. Transparency levels of 20 cm due to excess algae result in low oxygen levels and poor water quality. In addition, overfeeding causes: Water quality fluctuations Low dissolved oxygen/low ph levels in the morning High dissolved oxygen/high ph levels in the evening Factors impacting feeding At temperatures >32 C, feed intake increases while feed efficiency decreases. Feed passage through shrimp digestive system is very quick, resulting in poor dietary nutrient absorption. The best feed conversion/growth rates are obtained when oxygen concentrations exceed 4 mg/l. Water exchange/aeration Water is not exchanged during the first 60 days. Before being taken to the pond, water is treated in reservoirs. Later, a maximum of 10% water is exchanged per week. Aeration starts even prior to stocking. During the daytime, not all aerators are turned off. Maintaining water movement is recommended in order to promote shrimp movement, while preventing lesions during rotation. In Thailand, the biomass-aeration ratio is 1 HP: 600 kg biomass. Pallet aerators are recommended up to a maximum of 1.5m depth. Deeper ponds require turbo-type aerators. Use of bacteria/probiotics Hiring a microbiologist is suggested to work during 2 grow out cycles, in the search of the adequate bacteria to maintain proper organic matter levels, while displacing pathogenic bacteria. Bacterial use needs vary for each shrimp pond. April - June

7 Harvest Harvesting during the nighttime is not recommended since at this time ph tends to decrease. The best harvest time is in the afternoon, when ph is between 8.0 and 8.5. At these ph levels molting does not occur. During strong rains, Thai producers add limestone to their ponds in order to avoid molting, to offset the low ph caused by rains. Tumpis Edition Editors: Dagoberto Sánchez Carlos Ching Máximo Quispe April - June